Brittle fracture often leads to total failure of structures. Partial use of tougher material as crack arresters in a structure will be effective to avoid extensive failures. But the theoretical analysis of arresting mechanism and evaluation of crack arrestability of material are insufficient at present particularly for lack of consideration of dynamic effect. In this paper the brittle crack propagation and arrest in the duplex type crack arrester tests are experimentally and analytically discussed on the basis of dynamic fracture mechanics consideration using the techniques as was used in the a uthor's previous papers. It is concluded that for a crack to be arrested in the arrester material the minimum dynamic fracture toughness of the arrester material at the temperature should be larger than the dynamic stress intensity factor of the propagating crack.